Compounds having a large absorption in a range of from 550 to 620 nm, particularly those having a maximum absorption (λmax) in a range of from 550 to 620 nm are used as an optical recording material forming an optical recording layer of optical recording media, such as DVD-Rs.
There have been many reports on cyanine compounds having an indole ring because of their high sensitivity and capability of coping with increasing recording speeds in the above-described applications as an optical recording material. For example, cyanine compounds having a specific organic group introduced at the 3-position of the indole ring to cope with high-speed recording are reported in Patent Document 1 and Patent Document 2. Patent Document 1 discloses a cyanine compound having spiroalkane at the 3-position, and Patent Document 2 discloses a cyanine compound with benzyl at the 3-position.
Optical recording media have ever been required to achieve further increase in recording speed, and optical recording materials are also required to exhibit performance in response to such requirement
Patent Document 1: JP 2002-52829A
Patent Document 2: JP 2003-231359A